Custom view engine

When a Razor view is compiled, it inherits a ViewPage<T>, where T is the @model. So we can use reflection to figure out what type the view wanted, and select it.

public class ModelSelectorEnabledRazorViewEngine : RazorViewEngine
{
protected override IView CreateView(ControllerContext controllerContext, string viewPath, string masterPath)
{
var result = base.CreateView(controllerContext, viewPath, masterPath);
if (result == null)
return null;
return new CustomRazorView((RazorView) result);
}
protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath)
{
var result = base.CreatePartialView(controllerContext, partialPath);
if (result == null)
return null;
return new CustomRazorView((RazorView)result);
}
public class CustomRazorView : IView
{
private readonly RazorView view;
public CustomRazorView(RazorView view)
{
this.view = view;
}
public void Render(ViewContext viewContext, TextWriter writer)
{
var modelSelector = viewContext.ViewData.Model as ModelSelector;
if (modelSelector == null)
{
// This is not a widget, so fall back to stock-standard MVC/Razor rendering
view.Render(viewContext, writer);
return;
}
// We need to work out what @model is on the view, so that we can pass the correct model to it.
// We can do this by using reflection over the compiled views, since Razor views implement a
// ViewPage<T>, where T is the @model value.
var compiledViewType = BuildManager.GetCompiledType(view.ViewPath);
var baseType = compiledViewType.BaseType;
if (baseType == null || !baseType.IsGenericType)
{
throw new Exception(string.Format("When the view '{0}' was compiled, the resulting type was '{1}', with base type '{2}'. I expected a base type with a single generic argument; I don't know how to handle this type.", view.ViewPath, compiledViewType, baseType));
}
// This will be the value of @model
var modelType = baseType.GetGenericArguments()[0];
if (modelType == typeof(object))
{
// When no @model is set, the result is a ViewPage<object>
throw new Exception(string.Format("The view '{0}' needs to include the @model directive to specify the model type. Did you forget to include an @model line?", view.ViewPath));
}
var model = modelSelector.GetModel(modelType);
// Switch the current model from the ModelSelector to the value of @model
viewContext.ViewData.Model = model;
view.Render(viewContext, writer);
}
}
}

Rendering

Welcome, my name is Paul Stovell. I live in Brisbane and work on Octopus Deploy, an automated deployment tool for .NET applications.

Prior to founding Octopus Deploy, I worked for an investment bank in London building WPF applications, and before that I worked for Readify, an Australian .NET consulting firm. I also worked on a number of open source projects and was an active user group presenter. I was a Microsoft MVP for WPF from 2006 to 2013.